In optical computing, two types of memory are used. One is essentially the same as the primary memory of conventional electronic computers, and consists of one-bitstore elements. The other is mass optical storage, which is implemented with optical disks or holographic storage devices. Mass optical storage provides very high capacity and is in common use with electronic computers, with interfaces to electronic computing devices.
Read only optical disks work by changing the reflective surface of a recording media, typically by subjecting them to modulated laser light. They were developed by the entertainment industry for storage and reproduction of video and music. Only later were they adapted for computer user. Erasable magnetoptic disks are also now in use for computing applications.
With regard to holographic disks, the basic scheme is to arrange data as "pages" which are then recorded on holograms. To retrieve data, the appropriate page is reconstructed from the hologram by transmitting light through it to a photodetector. Materials, such as thermoplastics have been developed that allow for both writing and erasing of holograms.
Attempts to develop erasable optical media that will permit real time recording have been fairly successful. Certain media have been found to react to intense incident light, which represents an image, in a manner that permits an image to be recorded. For example, the media might change its refractivity or reflectivity in response to the image. Subsequent illumination of the material by lower intensity light reproduces the image. Another image is recorded by again subjecting the media to high intensity light representing that image.
Despite these attempts to develop real time media, a problem still exists with regard to providing the necessary optical input. A need exists for an optical recording unit that will provide real time optical input to an optical media.